In the immediate aftermath of the earthquake off the Japanese coast, about 100 of Japan's 6,000 network prefixes -- or segments -- were withdrawn from service. But they started reappearing on global routing tables just a few hours later. Similarly, traffic to and from Japan dropped by about 25 gigabits per second right after the Friday quake, but returned to normal levels a few hours later. And traffic at Japan's JPNAP Layer 2 Internet exchange service appears to have slowed by just 10 percent since Friday, according to Renesys.

"Why have we not seen more impact on international Internet traffic from this incredibly devastating quake? We don't know yet," Cowie wrote.

An unknown number of people were killed and whole cities devastated by what was one of the worst earthquakes in over 100 years. The quake, which initially measured 8.9 on the Richter scale, generated a huge tsunami that inundated parts of Japan and put almost the entire Pacific coastline on a tsunami alert.

The effects of the quake, in terms of human loss and economic damage, are expected to be huge. The quake also disrupted electricity supplies and knocked two nuclear power plants out of commission . One reason Internet connectivity appeared to fare better could be that undersea cables remained relatively untouched by the quake, unlike in 2006 when an earthquake in Taiwan resulted in a large number of major cable breaks, Cowie said.

This time, the only noticeable breaks were in two segments of Pacnet's EAC submarine cable system, Cowie said. The system, which is owned by a consortium of six companies, is designed to provide up to 1.92 terabits per second of capacity across the Pacific. The breaks led to outages in several networks in Japan, the Philippines and Hong Kong.

Sections of the Pacific Crossing undersea cabling system connecting the U.S to Asia also appear to have been damaged. A note posted on Pacific Crossing's website this morning noted that two of the cables are currently out of service.

Pacific Crossing's cable lading station in Ajigaura, Japan was evacuated as a result of the tsunami. No information is available about when restoration efforts will resume, Pacific Crossing said.

Renesys noted that "lingering" problems with landing station equipment could generate new problems over the next few weeks.

Even so, "it's clear that Internet connectivity has survived this event better than anyone would have expected," Cowie said. He noted that Japan's attempts to build a "dense web" of domestic and international Internet connectivity appears to have paid off. "At this point, it looks like their work may have allowed the Internet to do what it does best: route around catastrophic damage and keep the packets flowing, despite terrible chaos and uncertainty."